Using HP on hydreigon isn't too smart... maybe if you REALLY hate gastordon then HP grass but I don't see anything else it is worth using for..
cause it have access to 16 of 17 attacking types.
Maybe if you hate dealing with the accuracy and/or low PP of certain Moves (Focus Blast, for example) or want a Special option for a Move-Type it only has Physical options for (Rock, for example). Otherwise, it's only for ensuring you have broad Type coverage.
I agree with the puns... maybe give up on them when there aren't good ones.. or try at least some funny ones and easy to understood.. I though that all venusaur puns were MEH and didn't understand most of them.
Puns had gotten lame faster than they did in the anime, which is saying a lot...
This 3-Headed beast needs some support, so let's see what we can scrounge up...
Partners & Allies
Okay, first of all, Levitate makes any non-Mold Breaker EQ user a great partner in Doubles and Triples, especially if they have Storm Drain or Water Absorb to negate Surf. Quagsire and Mixed Gastrodon are prime examples. Cradily also makes a good partner in Triples with Hydrei' taking center stage due to Storm Drain and tanking capacity. Hydrei' in a side-role in Triples with a Flying Type or Levitate Ability Pokemon on the other side allows for EQ spamming. As a side note, I personally like the combo of using Hydreigon along with Exeggutor and Dodrio for a fun, multi-headed Pokemon Rotation-Battle gimmick...
Ghost Types are often good allies due to their immunity to Fighting, Resistance to Bug, and a few have Resistance to Ice (Froslass, Chandelure, & Jellicent). Water Types are also good choices since they Resist Ice, often carry Ice Type Moves (usually for Grass Types, but remember that they work wonders on Dragon Types, too), and several Resist Bug (Jellicent yet again, Empoleon, Mantine, Gyarados, Swanna, Poliwrath, Qwilfish, & Tentacruel). Rounding out the allies, Poison Types are, likewise, good allies since Hydrei' is immune to one key Poison-Type Weakness (Ground), they Resist Fighting and Bug, and a few Resist Ice, too (but they're already covered as Water Types - Tentacruel and Qwilfish).